Lapping machine

ABSTRACT

A spherical surface lapping machine wherein two counterrotating surfaces defining a plane are also orbited in the plane around a shaft by a crankshaft offset to provide a complex movement to the surfaces. A pair of cup-shaped laps, for engaging a spherical surface, are supported for individual axial rotation with drive wheels connected to each of the laps being held in friction contact with the rotating surfaces so as to impart a rotation to the laps, which rotation is periodically reversed and varied in speed as the individual drive wheels are selectively forced into contact with orbiting counter rotating surfaces.

United States Patent [191 Burkey Get. 16, 1973 LAPPING MACHINE Primary Examiner-Donald G. Kelly 75 I t Lee B k Y L lf. 1 nven or C In orba mda Cal Assistant Examiner-Howard N. Goldberg [73] Assignee: North American Rockwell Attorney-L, Lee Humphries et a1.

Corporation, El Segundo, Calif. 22 Filed: Mar. 20, 1972 [571 ABSTRACT Appl. N0.: 236,296

A spherical surface lapping machine wherein two counterrotating surfaces defining a plane are also orbited in the plane around a shaft by a crankshaft offset to provide a complex movement to the surfaces. A pair of cup-shaped laps, for engaging a spherical surface, are supported for individual axial rotation with drive wheels connected to each of the laps being held in friction contact with the rotating surfaces so as to impart a rotation to the laps, which rotation is periodically reversed and varied in speed as the individual drive wheels are selectively forced into contact with orbiting counter rotating surfaces.

10 Claims, 6 Drawing Figures mama ' PAIENTEUUCT 1 61975 SHEET 1 5 PAIENTEBBBT 1 61915 $765128 SHEET 30F 5 PAIENIED B 3,765,128-

SHEET SB? 5 CRANKSHAFT OFFSET lDRiVE PLATE FULL RIGHT FIG.6

LAPPING MACHINE BACKGROUND OF THE INVENTION necessary to remove more and more imperfections from the bodies of these rotors. Various prior art devices have been used in the past for lapping the spheres,

but with present day tolerance requirements, these machines are now inadequate.

One prior art machine is shown in U.S. Pat. No. 3,11 1,789, entitled Sphere Lapping Machine, by H. M. Harmon. The device of that patent utilizes three laps, each of which operate about an axis intersecting each other, with one of the laps'having a complex rotation and with each of the other two laps being able to disengage alternately so as to transfer the support of the lapped sphere between each one of the noncomplex laps while maintaining the center of the sphere in the same position. The aforementioned operation provides adegree of randomness to the lapping process, which randomness insures that every portion of the sphere is lapped equally. a

In U.S. Pat. No. 3,133,383, entitled Ball Grinding and Lapping Machine, by R. M. Chapman, which application is assigned to North American Aviation, Inc., now Rockwell International Corporation, the assignee of the present invention, there is shown a machine using three laps with each of the laps position approximately 120 apart around the ball, or sphere. In that application, one of the laps is rotatably oscillated, while the remaining two are simply rotated. It is applicant's contention that the greater the random motion, the more accuracy will be achieved in the lapping process. The major difference between applicants device and the aforementioned referenced devices in U.S. Pat. Nos. 3,111,789 and 3,133,383 is the use of a random motion imparted to each of the laps. Since the relationship between the three laps and the ball is fixed in both of the aforesaid patents, runout error must be absorbed by the lap drive and support mechanisms. This is accomplished by gimbaling. Due to the mass involved, it is hypothesized that the runout causes cyclic loads on the laps, thus causing some problems in achieving parts with less than five microinches T.I.R. out of roundness. Furthermore, because three laps are used, a lap distance equivalent to only 75 percent of the ball's diameter is exposed to the lap. In the present invention, employing two laps, a lap distance equivalent to over 90 percent of the balls diameter is exposed to the lap. The basic theory being that quicker and better accuracy can be obtained by increased wrap-around of the lap on the ball. In addition, it is believed thata greater degree of randomness in the lapping of the ball can be achieved by using the two laps of applicants invention instead of three laps taught in the aforesaid patents.

SUMMARY OF THE INVENTION In the present lapping machine, there are provided two counterrotating machine surfaces, which surfaces rotate in the same plane. Aside from rotation, there is provided an orbital movement to both of the rotating surfaces around a shaft by a crankshaft offset. A pair of cup-shaped laps, designed to engage the spherical surface under lap, are supported for individual axial r0 tation in a plane parallel to the plane of the rotating surfaces. One drive wheel is connected to each of the laps in a plane perpendicular to the rotating surfaces. Each drive wheel is held in friction contact with the rotating surfaces to thereby impart a rotation to the laps. The orbiting of the counter rotating surfaces causes the drive wheels, not only to vary in speed, but to periodically reverse their directions, thereby imparting to the laps a high degree of random motion. Each of the laps is comprised of a floating drive shaft which is driven by one or more ball bearings location on the periphery of the shaft.

From the foregoing, it can be seen that it is an object of the present invention to provide an improved lapping machine.

It is another object'of the present invention to provide a lapping machine wherein the laps are rotated at a random speed.

It is another object of the present invention to provide a lapping machine for lapping a spherical ball.

It is a further object of the present invention to provide a lapping machine wherein each-of the laps are periodically reversed in direction.

The aforementioned and other objects of the present invention will become more apparent when taken in conjunction with the following description and drawings which form a part of this application.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a top view, partially sectioned, illustrating the lapping machine;

FIG. 2 is a side view, partially sectioned, of the lapping machine of FIG. 1;

FIG. 3 is a front view of the machine illustrated in FIGS. 1 and 2;

FIG. 4 is a partially sectioned, enlarged illustration of one of the lap spindle assemblies used in this invention;

FIG. 5 is a schematic view of the counter-rotating surfaces showing their relative positions when the crankshaft offset 14 is at. a predetermined angle of rotation; and

FIG. 6 is a schematic view of the counter-rotating surfaces showing their relative positions for additional angles of rotation of the crankshaft offset 14.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring simultaneously to FIGS. 1, 2 and 3; a circular flat driving disc 12 is rigidly affixed to the end of a shaft or crankshaft offset 14 by means of a locking washer l7 and screw 16, with the screw 16 passing through a common center portion of the crankshaft offset 14. A second driving disc 10, having a diameter sub stantially larger than the disc 12, is rotatably mounted to the shaft or crankshaft offset 14 by means of a bearing 19 with both discs 10 and 12 concentrically aligned to share the common center portion of the crankshaft offset 14. A recessed opening 13 in the face surface of disc 10 receives the disc 12 and permits the two discs to rotate independently of each other while allowing the surface of disc 12 and the surface of disc 10 to define a plane. Shaft or crankshaft offset 14 is affixed to a shaft 26 by an offset throw 20 so as to form a crankshaft. As clearly illustrated in FIG. 2, the shaft 14 is parallel to but offset from the shaft 26 by the offset throw 20. As a consequence, the element 14 will be subsequently referred to as a shaft or crankshaft offset 14. A spacer 21 maintains the outer race of bearing 19 and disc 10 to a distance from the offset throw 20 to enable disc 10 to rotate freely without contacting the surface of offset throw 20. A spacer 22 (FIG. 2), similar to the spacer 21, prevents the offset throw 20 from contacting the outer race of bearing 27 and the inside face of drive wheel 24. A retaining lock ring 30, shown in FIGS. 1 and 2, restricts the lateral movement of the shaft 26 within the bearings 28. Shaft 26 is coupled to a drive motor 36 by means of a coupler 34 and a right angle drive 42. As can be readily seen in FIG. 2 (as well as in FIGS. 5 and 6 to be discussed later), the operation of the motor 36 rotates the shaft 26 to cause both of the discs 10 and 12 to revolve in orbital paths around the axis of the shaft 26 by the rotation of the crankshaft offset 14. This operation results since, as explained above, the disc 12 is rigidly affixed to the end of the crankshaft offset 14, which is in turn affixed to the shaft 26 by the offset throw 20, while the disc 10 is rotatably mounted around the disc 12 and to the crankshaft offset 14 by means of the bearing 19. In addition, since the shaft 26 is coupled to the drive motor 36 by means of the. coupler 34 and right angle drive 42, the disc 12 is also rotated in a direction and at a speed which are determined by the drive motor 36. A support member 29 supports the shaft 26 for rotation by means of bearing 28. A drive wheel 24 is mounted for rotation around the shaft 26 by means of bearing 27. An 0 ring 32 is affixed to the outer end surface of the drive wheel 24 and positioned to contact the inner rim 31 of the disc 10. A drive motor 38 operates through a right angle drive 35, by means of a pulley 37 and a drive belt 33 to drive the drive wheel 24 to, in turn, cause the O ring 32 to rotate the disc 10 around the crankshaft off set 14 in a direction and at a speed which are determined by the drive motor 38.

A lap support 50 is rigidly connected to a base 60 to support two lap spindle assemblies 40, which will be described in more detail in conjunction with the description of FIG. 4. Two motor controls 44 operate from a power source (not shown) to indpeendently control the speed and direction of rotation of motors 36 and 38 respectively. Support member 29 is fixedly attached to a sliding base 47, which base is constrained from movement in all but the axis parallel to the axis of the shaft 26 by means of sliding rails 48. Lower arm 46 operates an eccentric (not shown) to engage the sliding base 47 and drive disc assembly into operating position and for disengaging the drive disc assembly. The drive disc assembly basically includes the discs 10 and 12, crankshaft offset 14, offset throw 20, bearings 19, 27 and 28, spacers 21 and 22, drive wheel 24, 0" ring 32, shaft 36 and support member 29.

Referring to FIG. 4, in combination with FIG. 3, lap spindle assembly 40 is shown mounted to the support 50 by means of an outer member 80 which slidably fits into an opening 85 in the support 50. The outer member 80 has a ridge or rim 83 which acts as a limiting stop to prevent the outer member 80 from being pushed too far into the opening 85. A radial groove 84, around the outer periphery of outer member 80, is positioned to receive a locking pin 56. The locking pin 56 and rim 83 affect exact positioning of the lap spindle assembly 40 in support 50 whenever the lap spingle assembly 40 has to be removed to be serviced or adjusted. The outer member 80 supports a hollow, cylindrical inner bearing surface 79 for axial rotation by means of bearings 78. The cylindrical bearing surface 79 is held in position by means of a keeper ring 81. A drive wheel 87 is formed as an integral part of the hollow cylindrical bearing surface 79. The drive wheel 87 is fixed perpendicular to the axis of rotation of shaft 65. At one end of shaft 65 there is attached by means of threads 82 a cup-shaped lap or chuck 62. The cupshape of the lap 62 supports a spherical object 64, such as a gyro rotor or other type of ball. The shaft 65 is driven by the drive wheel 87 through a free floating drive comprised of ball bearings and 74. Ball bearings 70 rest in an indent 69 in the drive wheel 87 and in a corresponding indent 72 in a section 67 which is integral with the shaft 65. An end housing 76 is fixedly attached to the drive wheel 87 and forms a bearing surface for the ball bearing 74. The ball bearing 74 is inserted into the indent 72 in the end of shaft 65 to allow for radial movement of shaft 65 and lap 62, which radial movement compensates for any slight misalignments. A rubber 0" ring 77 affixed to the outer end surface of the drive wheel 87 provides the friction surface which rubs against the rotating plates or discs 10 and 12 to impart the axial rotation to the shaft 65. Referring to FIG. 5, the positions of the rotating discs 10 and 12 with respect to the drive wheels 77a and 77b which each contain an O ring similar to the 0" ring 77 affixed to the outer surface of the drive wheel 87 as shown in FIG. 4, is shown for the case when the crankshaft offset 14 is in the vertical or upper center position. In this case, both drive wheels 77a and 77b are at equal radii from the center of crankshaft offset 14. around which center discs 10 and 12 rotate. At this instant of time, as seen in FIG. 5, both of the drive wheels 77a and 77b make contact with the rotating disc 10. In this instance then, with radius R (between the crankshaft offset 14 and the drive wheel 77b) being equal to radius R (between the crankshaft offset 14 and the drive wheel 77a), the drive wheels will be rotating at the same speed. Their direction of rotation will be in opposition. At this instant in time, the O ring 32 on the drive wheel 24 is in contact with the rim 31 of disc 10 at the lowermost point, as shown in FIG. 2. As the shaft 26 rotates, the crankshaft offset 14 continues to rotate from this upper center position in the indicated counter-clockwise direction. consequently, the radius R between the crankshaft offset 14 and the drive wheel 77b will increase and the radius R between the crankshaft offset 14 and the drive wheel 77a will decrease. This, in turn, will cause drive wheel 77b to increase in speed while drive wheel 77a will decrease in speed. This varying of the speed of the drive wheels imparts a random motion into the laps.

Referring now to FIG. 6 wherein the crankshaft offset 14 is substantially shown in its farthermost right position with respect to drive wheel 77b. In this approximate position, the radius R is substantially reduced thereby allowing the drive wheel 77b to come into contact with the drive disc 12. Disc 12 is rotating in a direction opposite to that of the disc 10. Therefore, when the drive wheel 77b comes into contact with the disc 12, the drive wheel 77b will momentarily rotate in the opposite direction during the time that it is rolling on the surface of disc 12. At the point in time when, the radius R is at maximum, the wheel 77a is rotating at its highest speed.

From the foregoing, it can be seen that the wheels 77a and 77b are caused to rotate by the counterrotating discs and 12 as the crankshaft offset 14 is orbited by the rotation of the shaft 26 at a constant speed, and periodically each of the drive wheels are reversed in direction with respect to the opposite wheel. This particular random motion imparts a circularity to a sphere under lap which heretofore was unobtainable in prior art lapping machines. To make the motion of the system even more random,the speed of drive motors 36 and 38 can also be varied independently and, of course, the direction of rotation reversed.

While there has been shown what is considered to be the preferred embodiment of the invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims, to cover all such changes and modifications as fall within the true scope of the invention.

What is claimed is:

l. A lapping machine for lapping a spherical surface comprising in combination: I

two counter-rotating surfaces defining a plane;

means for orbiting and counterrotating surfaces in the defined plane;

first and second means for engaging the spherical surface;

means supporting said first and second means for individual axial rotation; and two drive wheels respectively coupled to said first and second means with said drive wheels being selectively in friction contact with said rotating surfaces so' as to impart axial rotation to said first and second means, said orbiting means causing said counter-rotating surfaces to selectively make contact with said drive wheels so as to periodically reverse the direction and speed of rotation of said first and second means.

2. The sphere lapping machine of claim 1 wherein said two counter-rotating surfaces are substantially concentric circular plates having different diameters, with the smaller diameter plate positioned to rotate within an opening defined by the larger diameter plate.

3. The sphere lapping machine according to claim 1 further comprising:

drive means operatively coupled to said counterrotating surfaces for rotating said surfaces at speeds independent of each other.-

4. The sphere lapping machine according to claim 1 wherein each of said first and second means comprises:

a cup-shaped chuck for engaging the spherical surface;

a shaft connected at one end to said chuck;

cylindrical bearing surface means rigidly connected to an associated one of said drive wheels, said cy-- lindrical bearing surface means having a hollow portion for receiving said shaft therewithin;

at least one indent on said shaft;

at least one indent in the hollow portion of said cylindrical bearing surface means;

a ball bearing positioned in each indent of said shaft and said cylindrical bearing surface means for rota- LII tionally locking said shaft to said associated drive wheel while allowing radial movement of said shaft to compensate for misalignments; and

an outer member for rotatably mounting said cylindrical bearing surface means in said supporting means.

5. A sphere lapping machine comprising:

a first shaft having a crankshaft offset on one end thereof;

a first disc fixedly attached to said crankshaft offset at the center of symmetry of said first disc;

a second disc having an opening defined thru the center thereof for receiving said first disc, said second disc rotatably mounted on said crankshaft offset;

first means coupled to said first shaft for rotating said first shaft in a first direction to cause said first and second discs to orbit around said shaft and to further cause said first disc to rotate in the first direction;

second means coupled to said second disc for rotating said second disc in a second direction counter to the first direction of said first disc;

third and fourth means for engaging a spherical surface;

support means coupled to said third and fourth means for allowing the individual axial rotation of said third and fourth means; and

first and second drive wheels respectively coupled to third and fourth means with said drive wheels being in friction contact with the rotating surfaces of said discs so as to impart axial rotation to said third and fourth means, the rotational and orbital movement of said discs causing the friction contact to selectively oscillate between the counter-rotating surfaces so as to periodically reverse the direction and speed of rotation of said third and fourth means.

6. The sphere lapping machine according to claim 5 wherein each of said third and fourth means comprises:

a cup-shaped chuck for engaging the spherical surface;

a second shaft connected at one end to said chuck;

cylindrical bearing surface means rigidly connected to an associated one of said drive wheels, said cylindrical bearing surface means having a hollow portion for receiving said second shaft therewithin;

at least one indent on said second shaft;

at least one indent in the hollow portion of said cylindrical bearing surface means;

a ball bearing positioned .in each indent of said second shaft and said cylindrical bearing surface means for rotationally locking said second shaft to said'associated drive wheel while allowing radial movemement-of said second shaft to compensate for misalignments; and

an outer member for rotatably mounting said cylindrical bearing surface means in said supporting means.

7. A sphere lapping machine comprising in combination:

two oppositely rotating surfaces defining a plane and rotating about a common center;

means for orbiting the common center of said surfaces;

first and second means for engaging a spherical surface;

means supporting said first and second means for iii- -dividual axial rotation; and

first and second drive wheels respectively coupled to first and second means, with said drive wheels being selectively in friction contact with said rotating surfaces such that the radii between the common center and the locations of friction contact of said drive wheels selectively vary to vary the speed and direction of rotation of said first and second means.

8. The sphere lapping machine of claim 7 wherein said two rotating surfaces are circular plates having different diameters, with the smaller diameter plate positioned to rotate within an opening defined by the larger diameter plate and in a direction opposite to the larger diameter plate.

9. The sphere lapping machine according to claim 7 further comprising:

drive means operatively coupled to said rotating surfaces for rotating said surfaces at speeds independent of each other.

10. The sphere lapping machine according to claim 7 wherein each of said first and second means comprises:

a chuck for engaging the spherical surface;

a shaft connected at one end to said chuck;

a cylindrical bearing surface means rigidly connected to an associated one of said drive wheels, said cylindrical bearing surface means having a hollow portion for receiving said shaft therewithin;

at least one indent on said shaft;

at least one indent in the hollow portion of said cylindrical bearing surface means;

a ball bearing postioned in each indent of said shaft and said cylindrical bearing surface means for rotationally locking said shaft to said associated drive wheel while allowing radial movement of said shaft to compensate for misalignments; and

an outer member for rotatably mounting said cylindrical bearing surface means in said supporting means. 

1. A lapping machine for lapping a spherical surface comprising in combination: two counter-rotating surfaces defining a plane; means for orbiting and counterrotating surfaces in the defined plane; first and second means for engaging the spherical surface; means supporting said first and second means for individual axial rotation; and two drive wheels respectively coupled to said first and second means with said drive wheels being selectively in friction contact with said rotating surfaces so as to impart axial rotation to said first and second means, said orbiting means causing said counter-rotating surfaces to selectively make contact with said drive wheels so as to periodically reverse the direction and speed of rotation of said first and second means.
 2. The sphere lapping machine of claim 1 wherein said two counter-rotating surfaces are substantially concentric circular plates having different diameters, with the smaller diameter plate positioned to rotate within an opening defined by the larger diameter plate.
 3. The sphere lapping machine according to claim 1 further comprising: drive means operatively coupled to said counter-rotating surfaces for rotating said surfaces at speeds independent of each other.
 4. The sphere lapping machine according to claim 1 wherein each of said first and second means comprises: a cup-shaped chuck for engaging the spherical surface; a shaft connected at one end to said chuck; cylindrical bearing surface means rigidly connected to an associated one of said drive wheels, said cylindrical bearing surface means having a hollow portion for receiving said shaft therewithin; at least one indent on said shaft; at least one indent in the hollow portion of said cylindrical bearing surface means; a ball bearing positioned in each indent of said shaft and said cylindrical bearing surface means for rotationally locking said shaft to said associated drive wheel while allowing radial movement of said shaft to compensate for misalignments; and an outer member for rotatably mounting said cylindrical bearing surface means in said supporting means.
 5. A sphere lapping machine comprising: a first shaft having a crankshaft offset on one end thereof; a first disc fixedly attached to said crankshaft offset at the center of symmetry of said first disc; a second disc having an opening defined thru the center thereof for receiving said first disc, said second disc rotatably mounted on said crankshaft offset; first means coupled to said first shaft for rotating said first shaft in a first direction to cause said first and second discs to orbit around said shaft and to further cause said first disc to rotate in the first direction; second means coupled to said second disc for rotating said second disc in a second direction counter to the first direction of said first disc; third and fourth means for engaging a spherical surface; support means coupled to said third and fourth means for allowing the individual axial rotation of said third and fourth means; and first and second drive wheels respectively coupled to third and fourth means with said drive wheels being in friction contact with the rotating surfaces of said discs so as to impart axial rotation to said third and fourth means, the rotational and orbital movement of said discs causing the friction contact to selectively oscillate between the counter-rotating surfaces so as to periodically reverse the direction and speed of rotation of said third and fourth means.
 6. The sphere lapping machine according to claim 5 wherein each of said third and fourth means cOmprises: a cup-shaped chuck for engaging the spherical surface; a second shaft connected at one end to said chuck; cylindrical bearing surface means rigidly connected to an associated one of said drive wheels, said cylindrical bearing surface means having a hollow portion for receiving said second shaft therewithin; at least one indent on said second shaft; at least one indent in the hollow portion of said cylindrical bearing surface means; a ball bearing positioned in each indent of said second shaft and said cylindrical bearing surface means for rotationally locking said second shaft to said associated drive wheel while allowing radial movemement of said second shaft to compensate for misalignments; and an outer member for rotatably mounting said cylindrical bearing surface means in said supporting means.
 7. A sphere lapping machine comprising in combination: two oppositely rotating surfaces defining a plane and rotating about a common center; means for orbiting the common center of said surfaces; first and second means for engaging a spherical surface; means supporting said first and second means for individual axial rotation; and first and second drive wheels respectively coupled to first and second means, with said drive wheels being selectively in friction contact with said rotating surfaces such that the radii between the common center and the locations of friction contact of said drive wheels selectively vary to vary the speed and direction of rotation of said first and second means.
 8. The sphere lapping machine of claim 7 wherein said two rotating surfaces are circular plates having different diameters, with the smaller diameter plate positioned to rotate within an opening defined by the larger diameter plate and in a direction opposite to the larger diameter plate.
 9. The sphere lapping machine according to claim 7 further comprising: drive means operatively coupled to said rotating surfaces for rotating said surfaces at speeds independent of each other.
 10. The sphere lapping machine according to claim 7 wherein each of said first and second means comprises: a chuck for engaging the spherical surface; a shaft connected at one end to said chuck; a cylindrical bearing surface means rigidly connected to an associated one of said drive wheels, said cylindrical bearing surface means having a hollow portion for receiving said shaft therewithin; at least one indent on said shaft; at least one indent in the hollow portion of said cylindrical bearing surface means; a ball bearing positioned in each indent of said shaft and said cylindrical bearing surface means for rotationally locking said shaft to said associated drive wheel while allowing radial movement of said shaft to compensate for misalignments; and an outer member for rotatably mounting said cylindrical bearing surface means in said supporting means. 